Allele and genotype frequencies for two tetrameric short tandem repeat (STR) loci were determined in two population samples, from Andalusia (S Spain; n = 127) and the Maghreb (N Africa; n = 40). After denaturing polyacrylamide gel electrophoresis, 14 alleles were identified for D12S391 and 13 alleles for D1S1656. No deviations from the Hardy-Weinberg equilibrium were detected. Some statistical parameters of forensic interest (H, PD, EC) were also calculated, and the data obtained for both populations were compared. Sequencing data of several intermediate D12S391 alleles designated 17.3, 18.3, and 19.3 are also presented.